Your receiver can use the PLIIx or Neo6 or any of Onkyo DSP modes to create surround ambiance from "any old normal CD" or other 2-channel source. Check the manual (I remember mine had something towards the end) for a description of each and recommendations which ones to use. Obviously "Movie" and "Cinema" work better for dialog-type content, and "Music" for everything else.
You'll find that for depending on content and even your mood you'll like some better than others. I use "all channel stereo" for background listening, for example.
Also, unless you play 'direct' mode, some sound should be sent to your sub even in stereo if you set front speakers to 'small'.
Enjoy the hobby!